7,184 research outputs found
Intermediates, Catalysts, Persistence, and Boundary Steady States
For dynamical systems arising from chemical reaction networks, persistence is
the property that each species concentration remains positively bounded away
from zero, as long as species concentrations were all positive in the
beginning. We describe two graphical procedures for simplifying reaction
networks without breaking known necessary or sufficient conditions for
persistence, by iteratively removing so-called intermediates and catalysts from
the network. The procedures are easy to apply and, in many cases, lead to
highly simplified network structures, such as monomolecular networks. For
specific classes of reaction networks, we show that these conditions for
persistence are equivalent to one another. Furthermore, they can also be
characterized by easily checkable strong connectivity properties of a related
graph. In particular, this is the case for (conservative) monomolecular
networks, as well as cascades of a large class of post-translational
modification systems (of which the MAPK cascade and the -site futile cycle
are prominent examples). Since one of the aforementioned sufficient conditions
for persistence precludes the existence of boundary steady states, our method
also provides a graphical tool to check for that.Comment: The main result was made more general through a slightly different
approach. Accepted for publication in the Journal of Mathematical Biolog
Construções geométricas com régua e compasso
TCC (graduação) - Universidade Federal de Santa Catarina, Centro de CiĂŞncias FĂsicas e Matemáticas, Curso de Matemática.Este trabalho tem o objetivo de mostrar aos mais leigos em matemática que a mesma nĂŁo Ă© apenas feita de operações de adição e subtração, mas mostrar que existem diversas formas de abordagem, sendo que este trabalho enfoca uma das particularidades, extremamente importante que Ă© a geometria construĂda com rĂ©gua e compasso. Temos por objetivo apresentar as construções geomĂ©tricas e suas demonstrações, usando para isso, toda a geometria euclidiana.Mostraremos que com estas duas ferramentas tĂŁo simples e tĂŁo antigas somos capazes de construir toda a geometria. Relatamos fatos de matemáticos envolvidos com a geometria de construção com rĂ©gua e compasso que começaram a pensar em fazer sĂł com uma das ferramentas por vez, o que resultou na geometria sĂł do compasso e em seguida a geometria da rĂ©gua
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